This invention relates to door hardware, and more particularly to hinges which allow a door to articulate outwardly from a door frame before being allowed to swing open.
Many large, enclosed industrial structures have access doors along their lengths to allow workers to access the interior of the structure for monitoring, maintenance and repair purposes. One such enclosure which has a plurality of doors is a wood veneer dryer, which dries wood veneers by heat. The doors in a veneer dryer allow access to various portions of the machinery, including rollers, contained within the dryer.
Each of these doors in a veneer dryer requires a seal sandwiched between the door and the door frame, the seal affixed either to the door or to the corresponding door frame. Such a seal prevents air from being drawn into the dryer, thereby reducing the potential for a fire, and also prevents the hot, acrid air produced within the dryer from escaping from the dryer into the surrounding environment. Further, the seals are needed to properly maintain pressure differentials within portions of the dryer itself. It is thus important to maintain these seals in very good condition.
There are two significant problems with these seals in current veneer dryers. First, the doors in most veneer dryers are hinged to the door frames in a standard manner, ie. by simple hinges which allow the doors to swing open in a typical fashion. This swinging action wears the door seals unevenly, and in particular, the portion of the seal closest to the hinged edge of the door wears quickly, as the door is opened and closed, relative to the other portions of the seal. Given the importance of these seals in a veneer dryer, the seals require constant monitoring and frequent replacement, costing the dryer operator money and lost time.
Second, most portions of veneer dryers, which are generally made of metal, naturally expand significantly when hot, and contract when cold. The amount of expansion, of course, depends largely on the temperature reached in the dryer, and the material used in construction of the dryer. The door of a dryer may expand and contract at a different rate than the door frame to which it is attached. This alters the pressure on the seal sandwiched between the door and the door frame.
An operator may try to compensate for this by trying to adjust the force exerted by the door against the door frame (ie. the door""s tightness) to try to maintain a constant pressure on the seal between them. Currently, operators try to accomplish this by adding or removing shims between the hinges and the door and/or door frame. This is an inaccurate, time consuming procedure which cannot be done when the dryer is in operation.
To limit the aforementioned uneven and premature wear on the door seals, therefore, it would be useful to provide an improved door hinge system which allows an operator to first move a veneer dryer door relatively straight out and away from the door frame before swinging the door open in a typical fashion. This would allow the door seal to wear relatively evenly, reducing the need for frequent replacement.
Further, to make it possible to adjust the force exerted by the door against the door frame (ie. to adjust the pressure on the seal), it would be helpful to provide associated means for allowing a door to be tightened or loosened against its frame while it is in a closed position.
The present invention provides a door hinge system for attaching a door to a door frame. Most broadly, the invention comprises, in combination, a linkage having a first end pivotally connected to a door at a first pivot axis and a second end pivotally connected to the door frame at a second pivot axis; and an arm pivotally connected at a first end to the linkage at a third pivot axis further from the door than the plane between said first and second axes. In this manner, the door can be moved outwardly relative to the door frame by moving the rod longitudinally towards said linkage, and then swung open in a normal fashion.
While the linkage can be connected directly to the door, in a retrofittable version of the invention, the first pivot axis passes through a first hinge portion attached to the door and the second pivot axis passes through a second hinge portion attached to the door frame. The linkage is accordingly connected to both of said hinge portions.
The arm itself may have a u-shaped bracket pivotally connected to the linkage and a threaded arm portion threaded into a block provided in the u-shaped bracket for receiving the threaded arm portion. A locking nut threaded against the block may secure the threaded arm portion to the u-shaped bracket. When the arm is fixed at its second end, shortening it by threading the threaded arm portion further into the block pulls against the linkage, tightening the door against the door frame.
In a further embodiment of the invention, a latch assembly is provided to the door which, in combination with the aforementioned hinge system, makes up a door assembly for tightening the door against the door frame in this assembly, the arm traverses the door and is connected at its second end to the latch assembly. The latch assembly has includes means for moving the arm from a first position pulling on the linkage to close the door to a second position pushing on the linkage to open the door. The arm can be shortened to tighten the door against the door frame (more particularly, against the seal sandwiched between the door and door frame), when the door is in a closed position. This can be accomplished by providing the arm with oppositely-threaded end portions and a central portion threaded onto each. Turning the central portion draws together, or forces apart, the ends of the arm.